Down comforters are well known in the United States and many other countries, including Europe, where the product originated. This lightweight, warm, natural bedding is desirable because of its fluffy, lofty appearance and significant durability.
Down comforters are manufactured with two basic sewing construction concepts, which each promote the comforter's aesthetic appeal and enhance its functionality in somewhat different ways. The two sewing constructions, referred to as controlled flow and random flow, control the distribution of the down and determine the loft of the down differently.
Controlled flow construction maintains an even distribution of down with a closed sewing pattern that restricts the movement of the down to relatively small areas within the body of the comforter. The most common configuration used is a consistent square box pattern. The size of the box usually varies between 6" and 20", with larger and smaller sizes possible. Many other closed sewing patterns have been used, such as tubes or channels, chevron scrolls, etc. In each case, the pattern defines an area where the down is uniformly distributed within the body of the comforter. Controlled flow construction produces an even distribution of down, but with only one, fixed, comfort level. It is not adjustable.
Random flow construction uses an open sewing pattern within the body of the comforter such that the down can flow to the edges, from top to bottom and side to side. This construction provides the maximum area for the down to loft to its thermal potential. It also provides the consumer the opportunity to adjust the down to his or her optimum comfort level. Different bedroom temperatures, consumer metabolism, and changing weather conditions are factors that determine varying comfort levels and the need to move or adjust the down within the body of the comforter. The available area within the comforter for the down to loft, furthermore, is maximized. Some examples of random flow sewing configurations are karo or line stitch (normally in a square pattern) ringstitch and diamond-shaped patterns. Many other variations and designs are possible which produce a variety in aesthetic appeal besides providing the important feature of adjustability that controlled flow constructions cannot provide.
Most sewing patterns in use today, whether controlled or random flow, use sewn-through stitches where the top and bottom fabric sections (forming the comforter envelope, which is known as the tick, are joined directly by the thread from the sewing machine. This sewing action within the body of the comforter creates what are known as "cold spots" because where the fabric is sewn together there is no down. The more sewing in the body of the comforter, the more cold spots. A piece of fabric known as a baffle (normally less than 1" in height) is sewn between the top and bottom fabrics. The down then lofts on either side of the baffle. Baffle sewing is an alternative to random flow construction because the baffles increase the available area for the down to loft and thereby maximize the comfort range, besides eliminating cold spots. The cost of labor for sewing baffle ticks, however, is quite high and additional down is required to fill the area created by the baffle. These additional costs effectively prohibit the use of baffles in controlled flow comforters.
Conventional random flow comforters are typically sized to hang down and cover the sides of the mattress as part of their aesthetic appeal. Through constant use and the force of gravity, however, the down will migrate from the center portion of the comforter and gather at the sides or the bottom. This migration of the down soon degrades the appearance and function of the comforter and compromises its intended adjustability. Thus, conventional random flow comforters require frequent re-fluffing to maintain effective distribution of the down. This task is time-consuming and can be difficult, particularly with luxury-sized comforters containing large amounts of down.
To some extent a similar problem exists for down (and feather) pillows, in which the down is pushed to one portion of the pillow, which typically occurs during actual use of the pillow, i.e. when the user is sleeping. This degrades the appearance and function of the pillow. Again, the typical remedy is redistribution of the down by fluffing, although this cannot be done, of course, when the user is sleeping. Discomfort in use results to a varying degree when the down is unevenly distributed in the pillow.